In-depth essays · #30 / 50 · Architecture, Consensus & Upgrades

The Southeastern Harbor Islands: How EVM Sidechains and Alt-L1s Differ from L2 Rollups

Why Polygon PoS, BNB Chain, Avalanche, Sonic, Berachain, Monad, and Kaia share the EVM but run their own consensus

Off the southeastern coast of Ethereum City’s mainland sit 13 island districts—including Polygon PoS, Gnosis, BNB Chain, Avalanche, Sonic, Cronos, Berachain, Monad, Sei, HyperEVM, Plasma, Kaia, and SKALE—linked to downtown by long sea bridges. Why are they placed on islands rather than on the mainland alongside L2 rollups?

1. What Unites Them with the City: The Ethereum Virtual Machine (EVM) and 0x Wallets

Every one of these 13 districts executes EVM bytecode, uses the same 0x... address format and wallet tools, hosts branches of major Ethereum protocols (Aave, Uniswap, USDT, USDC), and exchanges billions in liquidity with Ethereum mainnet across bridges.

2. What Separates Them from L2 Rollups: Independent Validator Sets

Mainland L2 rollups post transaction batches and state roots to Ethereum L1, borrowing downtown’s security. The harbor islands do not post blobs or proofs to Ethereum; instead, each island secures its ledger with its own independent validator set staking its native token (POL, GNO, BNB, AVAX, S, BERA, MON, KAIA, etc.).

That is why in Ethereum City you will see blue bridge buses crossing the sea bridges to these islands, but never orange blob trucks.

3. Unique Experiments Enabled by Sovereign Consensus

Running sovereign consensus lets each island specialize: Gnosis Chain uses dollar-pegged xDAI for everyday card payments; Berachain aligns validator rewards with DeFi pools via Proof of Liquidity; Monad and Sei push parallel EVM execution; and Plasma offers gas-free USDT transfers.

4. When Islands Move to the Mainland: Celo and Ronin’s Migration to L2

Notably, two chains that began life as independent networks—Celo (March 2025) and Ronin (May 2026)—chose to retire their standalone consensus and migrate onto the mainland as OP Stack Ethereum L2s.

Related districts in the city

Related glossary terms

This essay is an explainer written to help you read the city; it is not investment advice. Facts on this page are as of 2026-10 and may change. If you spot a mistake, please tell us through the contact page.